EP0862255A1 - Disconnector for surge arrester - Google Patents

Abstract

The arrangement includes an arrangement (3) recording a current flowing through the over-voltage protection device (1), and a switch-off arrangement triggered by the current measuring arrangement for separating the over-voltage protection device from a line supply. The arrangement records the electric energy received by the over-voltage protection device, and operates the switch-off arrangement when reaching a pre-settable energy quantity which is smaller or equal to the maximum power dissipation of the over-voltage protection device. The switch-off arrangement includes a breaker contact (2) connected in series to the over-voltage protection device.

Description

The invention relates to a disconnection device for surge arresters, comprising a the current through the surge arrester and one of these Device triggerable, causing the disconnection of the surge arrester from the network Switch-off device.

Various are used to derive overvoltages in power supply networks Components used. The most important examples are spark gaps, varistors, Suppressor diodes or the like. They are the voltage dependence of their electrical Resistance together. That means that they are below a threshold of being at them applied voltage have relatively high electrical resistances once the voltage however exceeds the threshold, become low resistance.

This property can be used to derive grid surges, the most common of Lightning strikes are caused to be exploited. For this purpose, said components in System leads between the phase conductors L1, L2, L3 and the ground PE as well installed between the neutral conductor N and the earth PE. The one mentioned earlier The voltage threshold is chosen so that the mains voltage is now constantly applied is below the threshold value, i.e. the components have high resistances in normal operation have and thus can flow little or no leakage currents. If an overvoltage now occurs, the voltage threshold value is exceeded, the components become low-resistance and the overvoltage energy is transferred to PE according to the components derived. An increase in the mains voltage to the - impermissibly high - value of Overvoltage can thus be avoided.

Depending on the energy content of the overvoltage, there are relatively high ones in the discharge case Surge arrester components flowing through and heating these currents.

Each discharge component is therefore exposed to thermal loads and can only up to to a certain extent, its maximum energy absorption capacity - depending on Resist component type, volume, material, etc. If it is loaded over this limit, there is destruction or at least damage to the component.

In addition to the relatively short-term overvoltages, such as those caused by lightning, there may also be longer mains voltage increases (so-called TOVs T emporary O ver V oltages), which of course also bring the discharge elements into their low-resistance discharge state.

The reason for this is as follows: One used to supply a system Low voltage network is powered by a transformer from a medium voltage network provided. Both star points - primary and secondary star point - of the transformer are earthed via a common earth resistance.

If an earth fault occurs in the medium-voltage network, one now occurs Current flow and, as a result, a voltage drop across the earth resistance.

But this is the secondary star point and thus the neutral conductor of the Low voltage network in its potential around said earth resistance drop raised. Subsequently, the potential difference between phase conductor earthing increases Low voltage network.

The TOVs are significantly lower in amplitude than lightning surge voltages, but can nevertheless reach a multiple of the nominal voltage phase conductor - earth. The most uncomfortable The property of TOVs with regard to arrester components is their relatively long time Exposure time. Such overvoltages can last a few hundred milliseconds take a long time, so stand in a usual 50Hz network for some periods on.

However, this is a long-acting leakage current and subsequently a high one thermal load on the arrester components.

In summary, an arrester component can be of either of the above types of overvoltage -Lightning strike and TOV- damaged or destroyed. As a result, the the component in question no longer has its full resistance after the overvoltage has subsided, so that even in normal operation no longer negligible currents flow to earth PE.

Such a defective component must therefore be recognized and one of the network means Arrester disconnector. So a new surge again against earth PE can ultimately be exchanged for the defective component and the arrester disconnector is switched on again.

For the constructive realization of a function just described Arrester disconnector, some suggestions have already been made.

EP-A1-261 606, EP-A1-613 226 and EP-A1-576 395 describe protective circuit arrangements which provide a switch-off device for each current path which is led from a mains line via an arrester, these current paths behind the switch-off device can be combined into a common grounding line. A monitoring device based on the residual current circuit breaker principle is installed in this common line. Each of the proposed arrester disconnectors provides a delay circuit in the secondary circuit of the summation current transformer, with which the switch is prevented from responding to currents caused by overvoltages; So a surge current resistance of the switch is achieved.

AT-PS-394 285 proposes to use the already existing residual current circuit breaker to monitor faulty arrester components. This is done in a simple manner by arranging the arresters behind the RCCB. Each current through a surge arrester represents a current to earth, that is, for the residual current circuit breaker a fault current causing it to trip, so that the residual current operated circuit breaker is switched off by impermissibly high arrester currents.

According to AT-PS-391 571 , one arrester disconnector is provided per arrester component. The functional principle of the disconnector is again that of a residual current circuit breaker. The current through the arrester is detected by a push-through converter. The current generated in the secondary coil of this push-through converter charges a capacitor; when a certain charging voltage is reached, the opening of a contact in series with the arrester component is triggered.

In all the proposed solutions, the damage or destruction of a Arrester component waited and only then because of the resulting impermissibly high arrester current the disconnection of the surge arrester or of the defective arrester component.

It is accepted that arrester components are only slightly above the Nominal voltage lying - and therefore rather harmless - overvoltages thermally destroyed become, which is the obvious disadvantage of the relatively high wear of Arrester components results.

The object of the present invention is therefore to provide an arrester disconnector at the beginning Specify the type cited, in which a thermal caused by the current flow Overload of an arrester component does not have to be waited for, but rather one such overload can be prevented.

According to the invention, this is achieved in that the device which from Surge arrester recorded electrical energy and when reaching a specifiable amount of energy that is less than or equal to the maximum Energy absorption capacity of the surge arrester to be protected is that Switch-off device actuated.

This means that before or when the maximum permissible heating of the arrester is reached Energy and thus the heat supply stopped, resulting in damage or destruction can be avoided.

According to a first embodiment of the invention it can be provided that the Switch-off device one in series to the surge arrester, by one Switch lock has actuatable interruption contact.

This represents a design possibility associated with particularly little material expenditure Switch-off device.

According to a second embodiment of the invention it can be provided that the Switch-off device a series connected to the surge arrester Surge protection device, preferably fuse, and one parallel to Surge arrester switched, operated by a switch lock short-circuit contact having.

The arrester is therefore not switched off by opening the contact but by Tripping an overcurrent protection device, preferably by melting one Securing what can be done by shorting the Surge arrester is caused. With fuses - compared to contacts - is open much easier way to realize a large "contact distance", so that Forming an arc and thus delaying or preventing the shutdown can be reliably prevented.

A particularly preferred embodiment of the invention can consist in that the Energy detection device is formed from a series circuit of a first circuit to form a signal proportional to the current through the surge arrester, a second circuit which integrates said signal over time and one Threshold detection circuit that operates the key switch.

This configuration option can be used in the case of arrester components, in which the on them falling voltage in the low-resistance state is approximately constant and known, be applied. A device for the detection of said voltage can be saved be, which significantly simplifies the entirety of the energy detection device.

In a development of the invention it can be provided that the circuit for forming a the signal proportional to the current through the surge arrester through a Current transformer, preferably a push-through converter, is formed.

This means that an amplitude that is electrically isolated from the arrester current can be significant smaller measuring current can be generated.

According to another embodiment, it can be provided that the circuit for Formation of a signal proportional to the current through the surge arrester Hall probe is formed.

This can also be a galvanically isolated signal, this time in the form of a voltage be generated.

Another training option of the invention may be that the Circuit for forming a proportional to the current through the surge arrester Signal is formed by an induction coil.

As with the Hall probe, such a current detection device also turns one into the Current proportional voltage received, here manufacturing and wiring essential are simpler than with a Hall probe.

Another feature of the invention may be that the integer circuit is a Rectifier circuit and a capacitor includes.

This allows a particularly simple, functionally reliable implementation of the Integrating function.

In this context it can also be provided that the integrating circuit is a Rectifier circuit and an operational amplifier connected as an integrator.

The gain of such an operational amplifier circuit is based on the selection of it forming components adjustable so that the amplitude of the output signal very easily Requirements of the downstream modules can be adjusted.

Furthermore, it can be provided that the threshold detection circuit by means of a Zener diode is formed.

Such a component has a precisely defined switching threshold that is constant over time, which ensures a constant switching behavior of the arrester disconnector can be.

Another variant of the implementation of the invention can be that the Threshold detection circuit is formed by an operational amplifier.

The switching threshold of such an arrangement can be particularly simple by selecting the Reference voltage can be set and also changed.

According to a further embodiment, it can be provided that the Threshold detection circuit by means of a transistor structure operated in the reverse direction is formed.

In contrast to the operational amplifier circuit just described, it requires one Transistor structure no operating voltage, so that the necessary for their generation Assemblies can be omitted.

According to a particularly preferred embodiment of the invention, provision can be made. that the circuit to form a current through the surge arrester proportional signal is followed by a filter circuit which is proportional to the arrester current Signal limited to frequencies less than or equal to the mains frequency.

This reduces the probability of false tripping in the event of short-term surges, which should actually be derived undisturbed, reliably reduced.

In this context, a further embodiment of the invention can provide that the filter circuit has low-pass or band-pass characteristics.

This eliminates the effects of high-frequency arrester currents on the Switch lock release reliably suppressed.

The invention will now be explained in more detail with reference to the accompanying drawings.

Fig.1a ein Prinzip-Blockschaltbild einer ersten Ausführungsform eines erfindungsgemäßen Ableitertrennschalters;

Fig.1b ein Prinzip-Blockschaltbild einer zweiten Ausführungsform eines erfindungsgemäßen Ableitertrennschalters;

Fig.2 das Prinzip-Blockschaltbild nach Fig.1a für die Anwendung bei Varistoren mit detaillierterer Darstellung der Energieerfassungs-Schaltung;

Fig.3 das maximale Energieabsorptionsvermögen eines Varistors in Form eines Strom/Zeit-Diagrammes;

Fig.4a-c Schaltbilder zweier praktischer Ausführungen eines erfindungsgemäßen Ableitertrennschalters mit einer netzspannungsunabhängigen Schaltschloß-Auslösung;

Fig.5 den Ableitertrennschalter nach Fig.4a,b mit einer netzspannungsabhängigen Schaltschloß-Auslösung und

Fig.6a-c verschiedene Ausführungsformen der die Belastung des Ableiterbauelementes erfassenden Schaltung.

The individual figures show:

1a shows a basic block diagram of a first embodiment of an arrester disconnector according to the invention;

1b shows a basic block diagram of a second embodiment of an arrester disconnector according to the invention;

2 shows the basic block diagram according to FIG. 1a for use with varistors with a more detailed representation of the energy detection circuit;

3 shows the maximum energy absorption capacity of a varistor in the form of a current / time diagram;

4a-c circuit diagrams of two practical designs of an arrester disconnector according to the invention with a switching lock release that is independent of the mains voltage;

Fig.5 the arrester disconnector according to Fig.4a, b with a mains voltage-dependent switch lock release and

6a-c show different embodiments of the circuit which detects the load on the arrester component.

The basic idea of the invention is a thermal overload of the Arrester component, which is caused by the current flowing through it prevent.

For this purpose, the amount of an arrester such as a varistor, suppressor diode or the like is provided. monitor supplied electrical energy and at the latest when the maximum is reached Energy absorption capacity of the component, but preferably something below this maximum absorption capacity, the arrester from the network separate.

A basic circuit diagram of an arrester disconnector with which these requirements are met can be shown in Fig.la. The disconnector according to the invention comprises a the current through the surge arrester 1 detecting device 3 and one of these Device 3 triggerable, the disconnection of the surge arrester 1 from the network effecting shutdown device. In the embodiment according to FIG Interrupting contact 2 connected in series with the surge arrester 1 to be protected formed, which is actuated by a switch lock 4.

Fig. 1b shows a second embodiment of the shutdown device. Here is the Shutdown device consisting of two parts, namely one in series with the surge arrester 1 switched overvoltage protection device 21, preferably as a fuse is executed, and a parallel to the surge arrester 1, by one Switch lock 4 operable short circuit contact 22.

The lines labeled a, b can be connected by any conductor Power supply network be formed. In the conventional three-phase network, the line a in the most common cases by a phase conductor L1, L2 or L3 and line b through the Protective conductor PE must be formed; within the meaning of the invention, however, it is equally possible to use said Series connection of surge arrester 1 and interruption contact 2 between others Wire pairs, e.g.: L1-N, L2-N, L3-N, L1-L2 or the like.

After the energy supplied to a resistive component according to the formula: W = u · i · t can be calculated, a device 3 is provided which detects the voltage present at the arrester 1 and the current through the arrester 1 and carries out the above calculation.

As soon as the calculated amount of energy has a predeterminable level Maximum absorption capacity or one just below the maximum Capacity is reached, the key switch 4 is actuated, which in further consequence in the embodiment variant according to Fig.la the break contact 2 opened and the arrester 1 is disconnected from the network; in the embodiment variant according to Fig.lb. Short-circuit contact 22 closed and the surge arrester 1 thereby has a low resistance is bridged. The short circuit that thus arises between lines a, b causes a large current through the overcurrent protection device 21, whereby this triggers and thus disconnects the arrester 1 from the network.

If the arrester 1 to be protected is a varistor, this is in practice is very often the case, a simplification of these basic circuit diagrams Fig.1a, Fig.1b be made. A varistor has that in its low-resistance state Property that the voltage drop across it a constant, almost from the current independent, known value.

The energy supplied is therefore only proportional to an unknown, the product i · t , ie the integral of the current over time. Therefore, to carry out the calculation described above only this product i * t need to be detected.

As shown in FIG. 2, an energy detection device 3 for varistors therefore only needs to have:
a first circuit 5 which forms a signal proportional to the current through the surge arrester 1,
a second circuit 6, which integrates said signal over time and a threshold detection circuit 7 symbolized by a comparator, which can actuate the switching lock 4, which it does at the latest when the energy supplied to the arrester 1 reaches the maximum absorption capacity. Instead of the interruption contact 2 shown, a short-circuit contact 22 can again come into connection with an overcurrent protection device 21, as shown in FIG. 1b, which was no longer explicitly shown in FIG.

The switch-off condition explained can be represented graphically in a particularly simple manner, as was carried out in FIG. The starting point for this diagram is the equation for the maximum energy absorption capacity of a varistor: W Max = u · i · t, with u = const => W Max prop. i · t

The straight line g is the set of all points in which the product i · t has a constant value which, multiplied by the constant voltage, gives the maximum energy absorption capacity of a varistor.

According to the invention, it is now provided that the shutdown characteristic of the arrester disconnector - no matter what their exact course looks like - with all their points below the straight line g lies. This means that the arrester to be protected can never be too high to damage it Amount of energy to be supplied.

A particularly simple practical implementation of the block diagram according to FIG. 2 is shown in Fig.4a, b shown and will now be described.

There is again the surge arrester 1 in its current path Break contact 2 is arranged. As shown in Fig.4a, the break contact is 2nd downstream of the surge arrester 1. This arrangement is by no means mandatory, rather, as can be seen from FIG. 4b, the interrupter contact 2 be upstream of the surge arrester 1. All-pole shutdown of the Arrester 1 by providing break contacts 2 actuated by the switching mechanism 4 its two feed lines - as shown in dashed lines in Fig. 4b possible.

Fig.4c shows the practical implementation of the block diagram of Figure 2, the Shutdown device is designed according to Fig.1b. As with dashed lines indicated, the overcurrent protection device 21 from the circuit of the arrester 1 removed and connected upstream of the entire system. When addressing the Switch-off device is thus not only the arrester 1 but the entire one Consumer system disconnected from the network. The overcurrent protection device 21 can with a such an arrangement should be formed by the existing house connection protection. The current through the arrester 1 is in these embodiments by means of a Current transformer 50 detected. Has turned out to be particularly cheap due to the small design a push-through converter proved.

As an alternative to a current transformer 50, however, any other possibility of Current measurement can be used, examples of which would be a Hall probe or a Induction coil in which the current through the arrester 1 induces a voltage, which is used directly as a current proportional signal.

The filter circuit 10 shown in broken lines is, as will be explained later, only optionally available and is not installed for the time being, the capacitor removed and the resistor replaced by a short circuit.

The signal supplied by the current sensors must now be integrated over time. Depending on the form of the signal supplied by the current sensor, corresponding components must be used for this. In the case of the embodiment according to FIG. 4, the signal proportional to the arrester current is again a current which, after rectification by the diode 61, can be integrated particularly easily over time by means of a capacitor 60: U _c = 1 / C · ∫i dt. The result the integral is in the form of the instantaneous capacitor voltage.

When using a voltage-supplying current sensor, a circuit is, of course, the Integrating voltage values can be used, the simplest example of which is an as Integrator-connected operational amplifier, cf. Fig. 6c.

The capacitor voltage is fed via a Zener diode 70 to a trigger relay 71, which trigger relay 71 is in operative connection with the switching lock 4. As soon as the Capacitor voltage exceeds the value of the breakdown voltage of the Zener diode 70, the capacitor 60 discharges through the trigger relay 71 and thus conducts the shutdown a, as shown by opening the interrupter contact 2 but also accordingly the basic circuit diagram of Fig.lb by short-circuiting the arrester 1 and the following An overcurrent protection device 21 connected upstream of the arrester 1 is triggered can.

The capacitance of the capacitor 60 and the breakdown voltage of the Zener diode 70 become dimensioned so that the shutdown in the inventive manner before reaching the maximum energy absorption capacity of the arrester takes place.

To switch the arrester disconnector back on, a manually operable one Restoring element 8 is provided. If the shutdown device by short circuit contact 22nd and overcurrent protection device 21 is formed, in addition to resetting the Switch lock 4 also a restart or an exchange of Overcurrent protection device 21 are made.

The type of switch actuation just described works independently of the mains voltage. but it is also within the scope of the invention to trigger the switch lock as in FIG. 5 shown to be dependent on the mains voltage.

The basic structure corresponds to that of FIG. 4 a, here the capacitor 60 discharges however, via a relay 72, which does not actuate the switching lock 4 directly, but via a contact 73 connects the trip relay 71 to the network. The trigger relay 71 speaks with it and actuates the key switch 4 that is operatively connected to it.

Instead of the breaker contact 2, the surge arrester 1 can again be used here bridging short circuit contact 22 in connection with a in series to Surge arrester 1 lying overcurrent protection device 21 are used.

As is customary with circuit breakers of all types, can also be used with an inventive Arrester disconnector a test device may be provided. This is formed by a second primary coil 51 of the current transformer 50, which is connected to the mains via a button 9 can be connected. When button 9 is pressed, an impermissibly high current is passed through the arrester 1 simulates the triggering when the switch is working properly causes.

4 and 5, the series circuit of surge arrester 1 and Interrupting contact 2 or the series connection of short-circuitable Surge arrester 1 and overcurrent protection device 21 always between L and PE used. However, this is - as already in connection with the explanation of FIGS. 1 and 2 mentioned - no restriction of the application of the invention to these two lines mean; said series connections can rather be between any two Line pairs of a power supply network must be installed.

The threshold value detection described so far by means of a Zener diode 70 can be used in the sense of FIG Invention also take place by other measures, as shown in FIGS. 6a-c. For the sake of clarity, only the wiring of the Tripping relay 71 shown, the remaining components of the invention Arrester disconnector, however, omitted.

In FIG. 6 a the Z diode is by a transistor structure 11 operated in the reverse direction formed, which in the simplest case consists of a single transistor. The base emitter path this transistor is connected in series in the reverse direction to the trigger relay 71, breaks -like a Z-diode- with a precisely defined voltage and thus enables a current flow through the trigger relay 71. By connecting several lines registered transistors, the breakdown voltage of the transistor structure 11 on easily increased.

Normally, only small currents can pass through the base-emitter path of a transistor are usually too low to cause the trigger relay 71 to respond will. It is therefore necessary to use further, more powerful transistor structures 11 Expand switching components; one possibility for this is shown in FIG. 6b.

The transistor structure 11 has transistors 12 and 13 and resistors 14 and 15 wired. A capacitor 16 can be advantageous to short-circuit interference signals. The Transistors 12 and 13 are arranged in a positive feedback circuit. The resistors 14 and 15 ensure a high-resistance connection of the transistor structure 11, as a result of which this does not act as a burden on capacitor 60 while it is charging. The Transistors 14, 15 are advantageously selected with a high current gain. If the If transistor structure 11 becomes conductive in its blocking direction, the voltage drop ensures Resistor 14 for controlling transistor 12 to be in the conductive state. The one then Current flowing through the resistor 15 leads to a voltage drop that causes the transistor 13 controls. An even larger current is then drawn via the resistor 14, since the voltage drop across transistor 13 in the conductive state is substantially lower.

The current actuating the trigger relay 71 thus flows almost completely in summary over the conductive emitter-collector paths of the transistors 12, 13 and can therefore without The amplitudes required for actuation of the trigger relay actuation cause damage accept.

According to a further embodiment of the invention shown in FIG. 6c Threshold value detection by an operational amplifier 20 connected as a comparator educated. The signal proportional to the arrester current is integrated by a another operational amplifier 17, which is connected by a circuit known per se Resistor 19 and a capacitor 18 is operated as an integrator.

The threshold value detection or. Integrating circuits can be used in any combination can be used: For example, the capacitor 60 in

6a, b are replaced by the operational amplifier 17 according to FIG. 6c; reverse is also a replacement of the operational amplifier 20 acting as a comparator with one Transistor structure 11 of Figures 6a, b is conceivable.

If excessively high overvoltages occur, the arrester must be undisturbed, i.e. without the arrester disconnect trips, can discharge. At a switch of the previous described type, this is only the case if the energy content of the Surge surge remains below the maximum energy absorption capacity of the arrester. However, the purpose of a surge arrester is to make surge voltages independent of theirs Energy content. even if they would destroy the arrester. The Surge current resistance of the arrester disconnector - the one discussed so far Design is only given in relation to "low-energy" surge surges accordingly also to extend to "high-energy" surge surges.

To achieve this, the invention provides that the one to be protected Arrester 1 flowing currents, the frequencies of which are greater than the mains frequency, that is of short-term surges, e.g. Lightning surges - are caused at the Calculation of the electrical energy supplied to the arrester 1 are disregarded.

In terms of circuitry, this is realized in such a way that the circuit 5 forms a current through the surge arrester 1 proportional signal, a filter circuit 10 is connected downstream, the signal proportional to the arrester current at frequencies smaller or equal to the network frequency. The TOVs mentioned at the beginning have a network frequency and therefore flow fully into the calculation of the energy consumption, the Arrester disconnectors therefore continue to respond to them.

In order to fulfill the aforementioned suppression function, said filter circuit 10 Have low-pass or band-pass characteristics and be designed for the network frequency.

In Fig. 2, this filter circuit 10 has been entered with dashed lines. The practical one Realization can be done by a simple passive RC circuit, as in FIGS. 5 represented, but also by any other known circuit that the required Has transmission properties take place.

Claims (15)

Disconnection device for surge arrester (1), comprising a device (3) which detects the current through the surge arrester (1) and a disconnection device which triggers the disconnection of the surge arrester (1) from the power supply and is characterized in that the device (3) the electrical energy absorbed by the surge arrester (1) is detected and the shutdown device is actuated when a predetermined amount of energy which is less than or equal to the maximum energy absorption capacity of the surge arrester to be protected is reached. Disconnecting device according to claim 1, characterized in that the switch-off device has an interruption contact (2) which is connected in series with the surge arrester (1) and can be actuated by a switch lock (4). Disconnection device according to Claim 1, characterized in that the disconnection device has an overvoltage protection device (21), preferably a fuse, which is connected in series with the overvoltage arrester (1), and a short-circuit contact (22) which is connected in parallel with the overvoltage arrester (1) and can be actuated by a switch lock (4) . Disconnection device according to claim 1, 2 or 3, characterized in that the energy detection device (3) is formed from a series circuit of a first circuit (5) for forming a signal proportional to the current through the surge arrester (1), a second circuit (6 ) which integrates said signal over time and a threshold value detection circuit (7) which actuates the key switch (4). Arrester disconnection device according to claim 4, characterized in that the circuit (5) for forming a signal proportional to the current through the surge arrester (1) is formed by a current transformer, preferably a push-through transformer. Arrester disconnection device according to claim 4, characterized in that the circuit (5) for forming a signal proportional to the current through the surge arrester (1) is formed by a Hall probe. Arrester disconnection device according to claim 4, characterized in that the circuit (5) for forming a signal proportional to the current through the surge arrester (1) is formed by an induction coil. Arrester disconnection device according to one of Claims 4 to 7, characterized in that the integrating circuit (6) comprises a rectifier circuit (61) and a capacitor (60). Arrester disconnection device according to one of Claims 4 to 7, characterized in that the integrating circuit (6) comprises a rectifier circuit (61) and an operational amplifier (17) connected as an integrator. Arrester disconnection device according to one of Claims 4 to 9, characterized in that the threshold detection circuit (7) is formed by a Zener diode (70). Arrester disconnection device according to one of Claims 4 to 9, characterized in that the threshold value detection circuit (7) is formed by an operational amplifier (20). Arrester disconnection device according to one of Claims 4 to 9, characterized in that the threshold value detection circuit (7) is formed by a transistor structure (11) operated in the reverse direction. Discharge separation device according to one of claims 4 to 12, characterized. that the circuit (5) for forming a signal proportional to the current through the surge arrester (1) is followed by a filter circuit (10) which limits the signal proportional to the arrester current to frequencies less than or equal to the mains frequency. Separating device according to claim 13, characterized in that the filter circuit (10) has a low-pass characteristic. Separating device according to claim 13, characterized in that the filter circuit (10) has a bandpass characteristic.

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